74 SFSR VIbrato tick

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Kcz5o, Feb 13, 2015.

  1. Kcz5o

    Kcz5o Member

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    ANy Help?

    I have a 74 super reverb and the vibrato sounds horrible. There is the tick problem and there is a snapping sound when I use the switch. I came across the fender "tick fix" bulletin and I installed an orange drop 715 series .01 uf 600v capacitor. That fixed the tick and the snapping but it seemed to have cut my volume in half and made the amp distort. I cut the capacitor out and the amp returned to normal. Sounds good if I don't use the vibrato but I would prefer that all the functions were working.

    Any idea why the fix had that effect?

    Thanks in advance.
     
  2. WaltC

    WaltC Member

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    Leakey cap? Placed wrong? Go back and verify the necessary location of the cap, the value of the cap recommended, and pick another cap (doesn't have to be an OD or anything special) and try again. Just from memory .... isn't the cap just supposed to bridge the 10 meg resistor on the LDR side to ground. This is just on the LDR side and takes noise out of the oscillator, not anything to do with the signal path of the amp.
     
  3. mark norwine

    mark norwine Member

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    correct
     
  4. zzmoore

    zzmoore Member

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    Man.....I never liked that cap "fix".
    I have never had that tick problem that was not cured with lead dress.....the trem tube cross talking to the phase inverter.
    Did you try separating those two tubes from each other..... Do you see how close the lead dress is.?
     
  5. swiveltung

    swiveltung Member

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    "Ticking" Vibrato


    • Fiberboard contamination: Dust, dirt, and junk can let the LFO signal leak into the audio path. Vacuum the dust and dirt away, and if it still persists, remelt the wax top and bottom with a hair dryer.
    • Solder blobs from eyelets touching insulating board: Sometimes excess solder drips out the bottom of an eyelet and can intermittetly contact the insulating board, can cause ticking. Remelt the eyelets and examine the board underneath for any blobs dripped down.
    • Funny ground on some SF Fenders; On one of the signal tubes, the cathode cap was placed on the tube socket, and wired to a ground lug on the vibrato cancel jack instead of across the resistor on the fiberboard. The vibrato shares this ground line, and can the vibrato current can cause audible ticking in the audio path. Rewire the cap to another ground or relocate it to the board.
    • Poor Signal wire layout: signal wires run too close to vibrato leads can pick up the LFO signal. Move them around and see if the ticking goes away.
    • Bad repair/replacement foot switch cable: the Fender footswitch cable is not two conductor; it's single conductor shielded, plus single conductor. The reverb wire is shielded, vibrato wire is not. This keeps vibrato out of reverb. If you retrofit with two conductor shielded, you get vibrato ticking onto reverb audio.
    • Sharp tick in vibrato oscillator: On neon/LDR Fenders, on the neon bulb side of the module there is a 10M to one side of bulb, 100K to the bulb; from the 10M straight across the board is the gnd point of the LDR. Put a 0.02 cap from 10M/bulb to the ground point; this works by filtering the output of the oscillator.
     
  6. OilsFan

    OilsFan Supporting Member

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    Is the vibrato "Tick" really a tick or can it be a "bumping" sound? Mine has gotten louder but I wouldn't call it a "tick" sound.
     
  7. zzmoore

    zzmoore Member

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    What happens when you turn the speed knob.?
     
  8. Kcz5o

    Kcz5o Member

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    Thanks for the input so far. Sorry for tha late response. I am waiting for some resistors from vintage amp repair before I open it up again. It may not be a tick sound, a bumping sound might me more accurate. The question I really had was why would installing the cap change the voume of the amp. Band ground solder joint? Yes the cap bridges the ten meg resistor to ground.
     
  9. WaltC

    WaltC Member

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    "The question I really had was why would installing the cap change the voume of the amp. Band ground solder joint? Yes the cap bridges the ten meg resistor to ground.
    "

    What I intended in my post was to let you know that if the cap is functioning properly, placed properly between the junction of the LED and 10M resistor and ground, and no other solder or lead related problems were introduced in the "fix", then the cap *could not* change the volume of the amp. Not possible.

    I've done this exact "fix" 10 or fifteen times over the years and in every case it made an improvement however slight, in some cases it fixed the "problem", and in many cases it was just one of several "fixes" that had to be done to clear up the tremolo noise including those that Swiveltung pointed out.
     

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